Magnetic shielding and x-ray image intensifier tube using same

ABSTRACT

An x-ray image intensifier tube is evacuated by means of an appendage magnetically confined glow discharge getter-ion vacuum pump. A shell of soft iron is disposed surrounding the magnet of the appendage pump for shielding the image intensifier tube from the stray magnetic field of the appendage pump. A coating of magnetic material on the envelope of the intensifier tube, in the region facing the pump, provides additional magnetic shielding for shielding the interior of the tube from the stray magnetic field of the pump to further improve the resolution of the image intensifier tube.

United'States Patent [191 Coon Oct. 9, 1973 [54] MAGNETIC SHIELDING FOREVACUATED TUBE COMPRISING PLURAL COATING OF BINDER AND MAGNETICPARTICLES [76] lnventor: Warren P. Coon, 3126 McKinley Dr, Santa Clara,Calif.

[22] Filed: Aug. 16, 1971 21 Appl. No.: 171,892

[52] US. Cl. 313/153, 315/8 [51] Int. Cl. H011 29/06 [58] Field ofSearch 117/234, 235, 239,

[56] References Cited UNITED STATES PATENTS 3,443,138 5/1969 Schwartz315/8 2,895,851 7/1959 Johnson 117/235 2,532,876 12/1950 Asche et al.335/303 Primary ExaminerRoy Lake Assistant Examiner-Darwin R.l-lostetter Attorney-Stanley Z. Cole [57] ABSTRACT 3 Claims, 3 DrawingFigures PAItNTEll "E 9 I975 INVENTOR. WARREN P. COON.

ATTORNEY MAGNETIC SI'IIELDING FOR EVACUATED TUBE COMPRISING PLURALCOATING OF BINDER ANI) MAGNETIC PARTICLES DESCRIPTION OFTl-IE PRIOR ARTl-leretofore, magnetically confined glow discharge getter-ion vaccumpumps have been appended to x-ray image intensifier tubes formaintaining a relatively high vacuum within the intensifier tube. A clamshell shaped shield of soft iron was disposed surrounding the magnet ofthe appendage pump to shield the interior of the intensifier tube fromthe stray magnetic field produced by the magnet of the pump.

However, it was found that the shell of soft iron surrounding the pumpwas inadequate to reduce the stray magnetic field within the interior ofthe intensifier tube to an acceptable level. In a typical example, themagnet of the appendage pump produces a magnetic field of 700 gausswithin the pump. With the soft iron shielding shell in place, the strayfield within the intensifier tube is reduced to a level of approximatelyfive gauss. However, five gauss is generally an unacceptable level.Attempts have been made to surround certain portions of the intensifiertube with'sheets of highly magnetic permeable material to further reducethe stray magnetic field within the intensifier tube. However, due tothe relatively complex compound curves of the envelope in the region ofthe pump it was exceedingly difficult to form the sheet metal shieldingmaterial to the required configuration. As a result, imperfect shieldingwas obtained. Therefore, it is desired to obtain an improved method andapparatus for shielding image intensifier tubes which will allow themagnetic shielding material to conform exactly to the complex curvesfound on the exterior of the intensifier tube in the region of theappendage pump.

SUMMARY OF THE PRESENT INVENTIO The principal object of the presentinvention is the provision of an improved magnetic shield and x-raybinder.

In another feature of the present invention, the exte- 1 rior of anevacuated electron tube is painted with a material which bonds to theenvelope and which will form a particle binder coating. A quantity ofmagnetic particles are sprinkled onto the coating of binder materialwhile the binder material is still wet to embed the magnetic particlesin the coating to form a magnetic shield conforming exactly to the shapeof the exterior surface of the tube.

In another feature of the present invention, a magnetic shieldingcoating is formed on the exterior of an evacuated electron tube bypainting the exterior portion of the tube with a rubber based paint andembedding a quantity of magnetic particles in the rubber based paintwhile wet.

Other features and advantages of the present invention will becomeapparent upon a perusal of the following specification taken inconnection with the accompanying drawing, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalline diagram, partly schematic, depicting an x-ray image intensifiertube incorporating features of the present invention,

FIG. 2 is an end view of the structure of FIG. 1 taken along line 2-2 inthe direction of the arrows, and

FIG. 3 is an enlarged view of the structure of FIG. 2 taken along line3-3 in the direction of the arrows with certain portions of theappendage pump and shield structure removed to show the magneticcoating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis shown a longitudinal sectional view of an x -rayimage intensifiertube 1 incorporating features of the present invention. The intensifiertube 1 includes an evacuated cylindrical envelope 2, as of glass, havinga spherically convex input face 3, as of glass or aluminum, disposed toreceive an x-ray image passing through the input face 3 to a similarlycurved x-ray converter/screen or scintillator 4 disposed adjacent theinput face 3 on the inside of the envelope 2.

The x-ray image converter screen 4 comprises an x-ray sensitive phosphorlayer which converts the x-ray image into a photon image. A photocathodelayer is also includedin the screen 4 to receive the photon image and toconvert same into an electron image which is emitter from the surface ofthe photocathode layer into the evacuated tube 2.

The electron images are embodied in the stream of electrons emitted fromthe x-ray converter screen 4. The stream of electrons is accelerated andfocused by means of a series of convergent electrostatic focusing lensstructures 5 through a hollow cylindrical anode electrode 6 onto acathode illuminescent intensifier screen 7 which converts the electronimage into an intensified photon image for viewing by an operator or foruse by photodetector equipment, not shown. A source of potential 8supplies the various operating potentials'to the electrodes 5, anode6,and fluorescent screen 7, the latter of which operates at anodepotential.

The evelope 2 is evacuated to a relatively low pressure, as of 10" torr,by means of an appendage magnetically confined glow discharge getter-ionvacuum pump 9 (FIG. 2) of conventional design. The appendage vacuumpump9 is connected in gas communication with the envelope 2 via a pumptubulation 11, as of glass, (see FIG. 3). The pump tubulation 11 isgenerally of cylindrical configuration and closed at its outer end via atransverse end wall 12. A collar 13 of magnetic material such as iron isbonded around the pump tubulation 11 to form one pole piece of themagnet structure of the appendage pump 9. A hollow cylindrical magnet 14(see FIG. 2) is disposed around the tubulation 11 and butts at one endwith the collar 13 and at the other end it is generally flush with theclosing end wall 12 of the exhaust tube 11. A disc of magnetic material,not shown, is disposed across the outer end of the magnet for fonn thesecond pole piece of the magnet. Anode and cathode pump electrodes aredisposed within the exhaust tube 11. The magnet structure produces anaxial magnetic field of approximately 700 gauss within the appendagepumpfor confining the glow discharge therein.

Two clam-shell shaped sheets of magnetic ally permeable material, suchas soft iron, are fitted around the appendage pump 9 to reduce the straymagnetic field produced by'the magnet of the pump 9. A clamshell shield15 of mild steel approximately 0.060 inches thick reduces the straymagnetic field within the envelope 2 of the image intensifier tube 1 toapproximately five gauss.

A five gauss stray magnetic field within the image intensifier tubeallows only a resolution in the intensified image of approximately 40lines or wires per inch. This is generally unacceptable for highresolution applications and it is desired to reduce the stray magneticfield to values which are substantially lower than five gauss.Accordingly, a coating of magnetic material 16, shown by cross hatchingin FIG. 3, is painted or otherwise formed on the exterior surface of theenvelope 2 in the region immediately adjacent and facing the pump 9. Thecoating 16 extends part way up the exhaust tubulation 11. The coatingfurther shields the interior of the envelope 2 from the stray magneticfield of the appendage pump 9.

In a preferred embodiment, the coating of magnetic permeable material 16is applied by painting the cross hatched portion of the envelope 2 witha first layer of a rubber based paint, such as Dow Corning type 92-009rubber paint (dispersion coating). While the paint is still wet, ironparticles of approximately 60 mesh or smaller are sprinkled onto thelayer of rubber paint to embed the iron powder in the rubber coating.Upon drying, the excess iron particles are dusted from the coating. Twoadditional layers of exactly the same configuration are successivelypainted onto the coated area 16 to an overall thickness of approximately0.015 inch. A final overcoat of rubber base paint is applied to improvethe appearance of the coating.

The resultant magnetic shield coating 16 greatly reduces the intensityof the stray magnetic field within the tube. More particularly, theaforedescribed coating 16 reduced the stray magnetic field within theenvelope 2 from five gauss to approximately 0.25 gauss, resulting in anincrease in resolution of the imageintensifier tube from approximately40 lines per inch to lines per inch.

The magnetic coating 16 of the present invention greatly facilitatesmagnetic shielding of the image intensifier tube as the coating exactlymatches the compound curves of the glass surface of the envelope 2,thereby minimizing the possiblity of leakage of magnetic field around orthrough the shield.

What is claimed is:

1. An evacuated electron tube comprising a nonmagnetic envelopecontaining anode and cathode electrode structures and amagnetically-permeable coating on at least a portion of said envelopefor shielding an adjacent interior portion of said envelope fromexternal magnetic fields,

characterized in that said coating comprises a layer of a bindermaterial on said portion of said envelope and a layer ofmagnetically-permeable particles embedded in the surface of said layerof binder material wherein said portion of said envelope has a pluralityof said coatings formed thereover in successive layers, each coatingcomprising a layer of said binder material and a layer of saidmagnetically-permeable particles embedded in the surface of said layerof binder material, thereby to provide increased shielding for saidtube.

2. The tube of claim 1 wherein each layer of binder material is arubber-based paint and each layer of magnetically-permeable particles isiron.

3. The tube of claim 1 further including a coating of binder materialover said plurality of said coating.

" UNITED Sl 'A'l'hb PALM Utklblb CER'HFICATE OF CORECTION Patent No 3764 841 Dated 1973 October 9 Inventor(s) Coon, Warren H.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the title, change "COATING" to ---COATINGS- On the Abstract page, addthe following:

-[73] Assignees Varian' Associates, a corporation of California. Q

In claim 1, change lines 7 to 17 to read as follows:

--characterized in that said covering comprises a plurality of coatingsformed in succession over said portion of said envelope, each coatingcomprising a layer of a binder material and a layer ofmagneticallypermeable particles embedded in the surface of said layer ofbinder material, whereby said plurality of coatings provide increasedshielding for said tube.--

Signed and sealed this 12th day of February 1974.

(SEAL) Attest: m w t H EDWARD M.FLETCHER,JR. I C. MARSHALL DANNAttesting Officer Commissioner of Patents

1. An evacuated electron tube comprising a non-magnetic envelopecontaining anode and cathode electrode structures and amagnetically-permeable coating on at least a portion of said envelopefor shielding an adjacent interior portion of said envelope fromexternal magnetic fields, characterized in that said covering comprisesa plurality of coatings formed in succession over said portion of saidenvelope, each coating comprising a layer of a binder material and alayer of magnetically-permeable particles embedded in the surface ofsaid layer of binder material, whereby said plurality of coatingsprovide increased shielding for said tube.
 2. The tube of claim 1wherein each layer of binder material is a rubber-based paint and eachlayer of magnetically-permeable particles is iron.
 3. The tube of claim1 further including a coating of binder material over said plurality ofsaid coating.